The present invention relates to a lens protector to be mounted on the periphery of an objective lens and an optical pick-up having the lens protector.
When an impact is unexpectedly applied to the optical pick-up during recording of signals on a CD or a DVD or during reproduction of signals therefrom, an objective lens or a signal-recording surface of an optical disc may be scratched. The optical pick-up having the function of condensing light for the CD and the DVD by the same lens has a problem that the objective lens collides with the optical disc owing to the difference in the working distance between the CD and the DVD and consequently the objective lens or the signal-recording surface of the optical disc may be scratched. Instead of the conventional semiconductor laser, development of a helium neon laser capable of recording more information than the conventional semiconductor laser is being made recently. In the helium neon laser, the interval between the objective lens and the optical disc is short. Owing to the degree of accuracy of the optical disc itself and the flexure of the optical disc during an operation, the objective lens and the optical disc may collide with each other. Thus there is a possibility that the objective lens and the signal-recording surface of the optical disc are scratched.
In a Blu-ray Disc and the like, the capacity and density of the optical disc have increased greatly in recent years. Thus the work space, namely, the interval between the objective lens and the surface of the optical disc has become very short when a focus servo is in operation. Consequently the danger of a possible collision between the objective lens and the optical disc has increased. Owing to the increase in the capacity and density of the optical disc, a protection layer covering the signal-recording layer of the optical disc has become thinner. Therefore the Blu-ray Disc and the like have a problem that owing to the collision between the objective lens and the optical disc, the signal-recording layer of the optical disc is liable to be scratched.
To solve the problem that the objective lens of the optical pick-up and the signal-recording surface of the optical disc thereof are scratched, the following proposals are made: A portion of the movable part of the actuator of the optical pick-up nearest to the optical disc is formed of the plastic softer than the plastic of the optical disc (refer to Japanese Patent Application Laid-Open No. 2-54433). The protector made of silicone rubber is mounted on the periphery of the objective lens (refer to Japanese Patent Application Laid-Open No. 11-312322). The cushioning material such as felt made of wool is mounted on the periphery of the objective lens (refer to Japanese Patent Application Laid-Open No. 2593998). The present applicant proposed the scratch prevention coating film (refer to Japanese Patent Application Laid-Open No. 2003-242703) formed on the periphery of the objective lens to prevent the optical disc from being scratched. The scratch prevention coating film contains urethane resin as its base component, polyurethane particles, and fluororesin powder.
However, in a recently developed optical pick-up (Blu-ray Disc or the like) using the DVD or the helium neon laser, a scratch on the signal-recording surface of the optical disc and that of the objective lens affect the reading performance of the optical disc adversely. Therefore it is difficult for even the protector, (disclosed in Japanese Patent Application Laid-Open No. 2-54433) of the optical pick-up, made of polyacetal resin softer than the plastic of the optical disc to completely prevent the signal-recording surface of the optical disc from being scratched. As described above, the scratch affects the reading performance of the optical disc adversely when the protector and the optical disc collide with each other.
It is difficult for the protector (disclosed in Japanese Patent Application Laid-Open No. 11-312322), made of the silicone rubber, which is mounted on the periphery of the objective lens to completely prevent the signal-recording surface of the optical disc from being scratched.
In the proposal that the cushioning material (disclosed in Japanese Patent Application Laid-Open No. 2593998) such as felt is mounted on the periphery of the objective lens, the cushioning material creeps and elastically deforms greatly. Thus it is difficult for the cushioning material to completely prevent the collision between the objective lens and the optical disc. As another problem of the cushioning material, dust such as waste thread is rubbed off the cushioning material and scatters in the optical pick-up, thus causing a failure.
The scratch prevention coating film (disclosed in Japanese Patent Application Laid-Open No. 2003-242703) containing the polyurethane resin is capable of coping with the problems of the above-described patent documents. But it is essential to mask the scratch prevention coating film in the manufacturing process. In the Blu-ray Disc using a very small objective lens and lens holder, it is difficult to mask the scratch prevention coating film when the diameter of the objective lens is not more than 5 mm.